A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In addition to EUV radiation, radiation sources used in EUV lithography tend to generate contaminant material that may be harmful for the optics and the working environment in which the lithographic process is carried out. Hence, in EUV lithography, a desire exists to limit the contamination of the optical system that is arranged to condition the beams of radiation coming from an EUV source. To this end, it is known to use a so-called rotating foil trap, for instance, as disclosed in U.S. Pat. No. 6,838,684. A typical foil trap uses a high number of closely packed foils that are aligned generally parallel to the direction of the radiation generated by the EUV source. Contaminant debris, such as micro-particles, nano-particles and ions can be trapped in walls provided by foil plates. Thus, the foil trap may function as a contamination barrier that traps contaminant material from the source. Generally, these foil traps are designed to have a sufficiently large dimension to trap virtually any contaminant particle traveling through the trap. Indeed, a large fraction of debris is captured since the velocity directions are mostly non-parallel to the foil plates so that impact of the contaminant material follows eventually. Also, smaller particles travel in typical random diffusion-like paths in which most of the particles are trapped eventually. However, a small fraction of particles travel in a direction and at a velocity that allows the particles to travel through the foil trap, which may cause undesired contamination of the optics. These are mostly micro and nanometer sized particles traveling at speeds <1000 m/s. Such particles may be stopped using a rotating foil trap. However, some of these particles have a velocity that is too high to be stopped by the rotating foil trap (typically this is the case for nanometer sized particles and for ions/fast neutrals). To improve the debris mitigating function of the foil trap, electromagnetic deflecting fields have been proposed.
However, a rotating foil trap functions as a rotor in a static electromagnetic field, which may impede the function thereof and cause undesired inhibiting of the foil trap rotation.